A follow-up survey by Vanclay and Hely (1997) found
the number of drills that could handle more than
2 t ha1 of stubble had almost doubled to 28% over the
3-yr period. Of more concern was that only 7% of drills
in the Central West of New South Wales could handle
stubble of 3 t ha1. A considerable disincentive to
increased stubble retention is the high cost of tillage
and sowing machinery to handle stubble densities
greater than 3 t ha1. This amount of stubble can be
left after just 2 t ha1 of wheat have been harvested.
Adoption of stubble retention will continue to be slow,
notwithstanding acknowledged benefits to resource
conservation, while there are real and perceived financial
disincentives such as cost of machinery changeover as
well as uncertain benefits for their farmprod uction
system. Farmers are reluctant to commit additional
scarce funds to purchase new machinery suitable for
handling high stubble densities during the testing phase
of the practice on their farm. Farmers will only purchase
new equipment if the practice is found to be better than
what they are currently doingto rotate around the shank. Factors contributing to stubble
rotation are: a large vertical clearance of at least 600mm; a
shank of circular cross-section of 50mm diameter; short
stubble length; and tines with a 708 rake angle.
The findings of Slattery and Riley (1997) demonstrate
the opportunities for improving the stubble handling
performance of tillage and sowing equipment. This
investigation examines the effect of these factors on the
flow of wheat stubble through a scarifier and a combine
drill that are typical of the implements owned by many
farmers in central NSW.
The study involved assessing the effects of straw
length, tine spacing, placement and shape on the ability
of implements to handle stubble levels exceeding 3 t ha1
where 80% of the standing stubble exceeded a straw
length of 400 mm. The implements used for the study
involved a Napier Grasslands scarifier with ‘edge-on’
tines with a vertical clearance of 500 mm, and a John
Shearer combine drill that was fitted with Primary Sales
Australia ‘C-shaped’ coil tines with a vertical clearance
of 400 mm.